1. Field of the Invention
The present invention relates generally to a switching power supply wherein a plurality of switching circuits connected parallel to one another perform respective switching operations to convert a power supply voltage into a controlled voltage.
2. Description of Related Art
An electronic control unit (ECU) of a vehicle has a switching power supply which boosts a power supply voltage of a battery. Therefore, even when the voltage of the battery is lowered due to cranking in the vehicle, the ECU can be normally operated while receiving a controlled voltage higher than the battery voltage from the switching power supply. The ECU performs many types of operations, and the number of operations has been recently increased. Therefore, the size of the ECU is also increased, and the operating current consumed in the ECU has been increased. To smoothly operate the ECU, it is required to increase the quantity of current supplied from the switching power supply.
To supply a large quantity of current to an ECU, a multi-phase DC/DC converter type switching power supply has been disclosed in Published Japanese Patent First Publication No. 2007-6669. In this power supply, a plurality of switching circuits corresponding to phases are connected parallel to one another, an input voltage of a battery is boosted in each switching circuit, and boosted voltages are applied to a single current supply line. Therefore, an electric current set at a controlled voltage higher than the battery voltage can be supplied from the line to an ECU.
However, to protect the switching circuits, it is required to detect an over-current flowing through each switching circuit in an over-current detector and to limit the current of the switching circuit in a current limiter. Therefore, each switching circuit needs one over-current detector and one current limiter As a result, the manufacturing cost and size of the switching power supply are undesirably increased.